Reaction mechanism studies will be continued with the following flavoenzymes; p-hydroxybenzoate hydroxylase, melilotate hydroxylase, lipoyl dehydrogenase, lactate monooxygenase, D-amino acid oxidase, and xanthine oxidase. The work is aimed at elucidating the role of flavin peroxides in hydroxylation reactions, and in the elucidation of the reaction steps involved in flavin-catalyzed dehydrogenation reactions, with particular reference to carbanion production, covalent intermediates of flavin and substrate, and charge transfer interactions. Considerable use will be made in these studies of chemically modified flavins which will be introduced into the enzymes in place of the natural coenzymes. In corollary experiments the chemical reactivity of 5 deazaflavins and 5 thiaflavins will be explored to test their suitability as flavin models. BIBLIOGRAPHIC REFERENCES: The Mechanism of Flavoprotein Catalyzed Dehydrogenation Reactions. V. Massey and S. Chisla, Proceedings Tenth FEBS Meeting 1975, p. 145. Role of Oxygenated Flavins in the Catalytic Reaction of p-Hydroxybenzoate Hydroxylase. B. Entsch, D.P. Ballou and V. Massey, in T.P. Singer (Ed.) Flavins and Flavoproteins, Elsevier Scientific Publishing Company, Amsterdam, 1976, p. 111.